Prosecutors sought the highest possible jail terms for three al-Jazeera English journalists on trial in Egypt, after accusing them, in their closing statements on Thursday, of making "a devilish pact" with the ousted Muslim Brotherhood.

Mohamed Fahmy, Peter Greste and Baher Mohamed now face prison sentences worth 15, seven and 15 years, after being held since December on charges of smearing Egypt's reputation, aiding the Brotherhood, and doctoring footage.

In the trial's 11th session, the prosecution finally closed its case, claiming that the three journalists had collected material from the Muslim Brotherhood and edited it to imply that Egypt was engaged in a civil war. The lead prosecutor, Mohamed Barakat, said al-Jazeera's reports on sexual assaults and street protests were among those aimed at smearing Egypt's reputation in the outside world.

"Freedom of expression does not mean the freedom to lie and spread false information," said Barakat.

The prosecution did not specify which raw footage or news packages had been doctored. In previous sessions, its evidence has included footage of horses taken from Sky News Arabia, a BBC documentary about Somalia and a press conference from Kenya. It also included dozens of raw videos of al-Jazeera interviews with figures from all sides of Egypt's spectrum – including the Muslim Brotherhood, the group that led Egypt until last July, but which has since been banned.

Al-Jazeera and, particularly, its Arabic wing is hated by pro-government Egyptians for its perceived bias in favour of the Brotherhood and for giving a voice to its supporters.

But in his defence on Thursday, Fahmy's lawyer, Khaled Abou Bakr, stressed that it was a reporter's job to interview activists of all political stripes – and to prosecute them for doing so was essentially to place journalism itself on trial.

"This is not a trial of these defendants alone – this is a trial of all journalists," said Abou Bakr.

"If you go and film someone saying: 'Down with the president,' that doesn't mean that you agree with it."

Shouting from the defendants' cage during a recess, Fahmy himself said that his trial was an affront to any journalist working in Egypt. "If we're in jail because we called [Egypt's 2013 regime change] a coup, why aren't CNN and the BBC in the cage?" he said. "Why isn't every journalist in the cage?"

In a detailed defence, Abou Bakr said the prosecution's case was severely flawed because its key witnesses had admitted in court that they were not qualified to judge whether the journalists had endangered Egypt – contradicting the central claims of the written testimonies they had supplied in the run-up to the trial.

Abou Bakr also highlighted a string of procedural flaws in the prosecution's case, ranging from the failure to allow defence lawyers access to all the prosecution's evidence; an inability to pinpoint any specific video that proved the accusations; and the uncertainty about which of the defendants' equipment belonged to whom.

Following a brief speech by Greste and Mohamed's lawyer, Yusri Sayed Sami, who repeated many of Abou Bakr's points, the trial was adjourned until 16 June – when the lawyers of several students indicted alongside the three journalists will be allowed to make their defence.

This raises the prospect of a verdict by the end of June, which was welcomed by Greste's younger brother, Mike, who has flown from Greste's home in Australia to attend the trial. "With any luck we're on the home straight, and with two more sessions we could be finished," said the younger Greste at the end of Thursday's proceedings. "But it's the judge that needs to be convinced of their innocence."

A fourth al-Jazeera journalist, Abdullah Elshamy, has been under arrest without charge in a separate case since August. To raise awareness for his case, Elshamy has been on hunger strike for more than 130 days. As punishment, he was recently moved to solitary confinement.